The present invention relates to random number generators (RNGs), in particular to generators based on the intrinsic randomness of quantum observables in multimode laser cavities with variable gain or loss.
Random numbers are by definition unpredictable, and a sequence of random numbers shows no predictable patterns. A random number generator (RNG) is a computational or physical device designed to generate random numbers. RNGs can be classified in pseudo-RNGs (PRNGs), which are computational algorithms, and true-RNGs (TRNGs). TRNGs are physical devices and can be subdivided into classical RNGs (CRNGs) based on classical processes such as chaotic dynamics that may be difficult to predict but are in principle deterministic, and quantum RNGs (QRNGs) based on quantum effects.
Current commercial RNG devices are based on the spatial distribution of single photons [1], chaotic dynamics in semiconductor lasers [2], CMOS metastability [3], single photon detection in arrays of single photon detectors [4], and phase diffusion in semiconductor lasers [5,6], among many other schemes.
The patent application “ultrafast quantum random number generator and system thereof” by Pruneri et al [5] discloses a QRNG based on measuring quantum phase diffusion in a pulsed single-mode semiconductor laser. By modulating the laser from below to above threshold, optical pulses with nearly identical intensities and completely randomized phases are generated. Then, by using an external interferometer, the random phases are translated into random amplitudes, which can be digitised with a proper detector. Instead of one laser source and an interferometer, two laser sources can be used together with a combiner. The technique allows for ultrafast operation regimes, and recent publications have shown bitrates of 40-Gbps [7,8]. However, the need for an external interferometric element or two lasers that are spectrally matched in emission and coupling optics complicates the layout as it increases the number of elements, the overall dimension of the QRNG device, and, in some cases the performance of the QRNG is affected by the stability of the components. For example, in the case of the two lasers their emission wavelength spectra have to be narrow (single mode), matched and maintained over time and this is not always easy to achieve due to intrinsic instability and environmental changes.
There is thus a need of a smaller form factor RNG source, with reduced dimensions (footprint) that maintains the high speed and quantum mechanical entropy properties.